In recent years, electroluminescent devices (hereinafter referred to as EL devices) have received attention as light-weight and thin light emitting devices of the surface-emitting type. The EL devices roughly are categorized into organic EL devices and inorganic EL devices. In the organic EL devices, a direct current voltage is applied to a luminescent material made of organic material, and electrons and holes are recombined to emit light. In the inorganic EL devices, an alternating current voltage is applied to a luminescent material made of inorganic material, electrons accelerated in an electric field as high as 106 V/cm are made to collide with a luminescence center of the inorganic luminescent material to excite the inorganic luminescent material, and the inorganic luminescent material emits light during a process of relaxing the excitation.
The inorganic EL devices are categorized into: dispersion-type EL devices (see JP 2006-120328 A) including a light-emitting layer formed by dispersing inorganic luminescent particles in a binder made of polymer organic material; and thin-film-type EL devices including a thin light-emitting layer with a thickness of approximately 1 μm obtained by thinning an inorganic luminescent material, with an insulating layer being provided on one or both sides of this thin light-emitting layer.
Among these, the dispersion-type EL devices have been gaining attention because they consume less power, and they are easy to produce, which is an advantage in reducing production cost.
However, an alternating current voltage is used for the conventional inorganic EL devices, and a high alternating current voltage is required to drive them. Thus, to be used in high-definition display apparatuses, the conventional inorganic EL devices have many problems in that, for example, they are incapable of active-matrix driving and have insufficient brightness and efficiency.
In view of the foregoing, the present inventors have invented a light emitting device that emits light by applying a direct current voltage to luminescent particles made of inorganic material and recombining electrons with holes in the luminescent particles. FIG. 7 is a cross-sectional view of a light emitting device 100. The light emitting device 100 shown in FIG. 7 includes a back electrode 102 and a transparent electrode 103 facing each other, luminescent particles 104 sandwiched between the back electrode 102 and the transparent electrode 103, and a substrate 101 for supporting the back electrode 102. A direct current power supply 106 is connected electrically to the light emitting device 100 to apply a direct current voltage thereto. In this configuration, however, electrically-connected portions between the electrode 102 and the luminescent particles 104 and between the electrode 103 and the luminescent particles 104 are few, causing a problem in that it is difficult to supply a sufficient amount of carriers to the luminescent particles 104. As a result, sufficient brightness cannot be obtained.